#define _CRT_SECURE_NO_WARNINGS
#include<iostream>
#include<vector>
using namespace std;


//Definition for singly-linked list.
struct ListNode {
	int val;
	ListNode* next;
	ListNode() : val(0), next(nullptr) {}
	ListNode(int x) : val(x), next(nullptr) {}
	ListNode(int x, ListNode* next) : val(x), next(next) {}
};

class Solution {
public:
    ListNode* swapPairs(ListNode* head) {
		ListNode* dummyHead = new ListNode(0);
		dummyHead->next = head;
		ListNode* cur = dummyHead;
		while (cur->next != nullptr && cur->next->next != nullptr) {
			ListNode* tmp = cur->next;
			ListNode* tmp1 = cur->next->next->next;
			cur->next = cur->next->next;
			cur->next - >next = tmp;
			cur->next->next->next = tmp1;
			cur = cur->next->next;
		}
		return dummyHead->next;
    }
};